Il 03/04/2014 19:08, Lukáš Czerner ha scritto:
However if we're talking about raw file system images in files in
the host, then much better solution would be to use fsck. Ext4
already has option -E discard which will send a discard down for
ever free range (similarly as fstrim would do on mounted file
system). I suspect that other fs utilities might have similar
functionality.
Of course in order for it to work you need a layer to translate
discard requests to punch holes to the underlying file system (such
as loop device for example). But I think that if there is enough
interest we might do this directly from e2fsck when we notice that
we're running on the file rather than block device.
The e2fsck can also be done from within libguestfs easily. libguestfs
runs within a VM so QEMU would handle the translation to hole-punching.
But fstrim is much faster than e2fsck.
From Richard's description, what seems to happen is that ext4 FITRIM
scans the filesystem and prepares the discard requests; but then it
sends them down to the filesystem after the ioctl has finished. Does
that make any sense? And would that be considered a bug?
Paolo
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